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Poorly soluble drugs constitute more than 60% of currently marketed pharmaceuticals with over two‐thirds of promising new chemical entities failing to enter a clinical setting due to solubility issues. Although oral formulations have made some impact, alternative enhancement strategies for administration of such molecules are actively sought. Over the last decade, innovation on a global scale has enabled the expansion of the frontiers of microarray patches (MAPs) further than ever before. Initially designed to load low doses of hydrophilic and potent therapeutic agents, MAPs are now becoming a viable strategy for the immediate and long‐acting delivery of poorly soluble drugs through the skin. This together with the advantages of transdermal administration over the oral and parenteral routes, make of MAPs an appealing platform for the development of products with increased patient compliance. Undoubtedly, MAPs will soon become a readily available therapeutic alternative, and experts from academia, industry and regulatory bodies are working together aiming to facilitate the progression of MAPs toward safe and effective clinical use. This review aims to highlight the ability of MAPs to deliver poorly soluble actives, discuss the mechanisms behind in‐skin drug absorption, and evaluate the future direction of the field.

Vitamin B12 plays an essential role in one-carbon metabolism in the human body. A deficiency in this vitamin can lead to severe haematopoietic and neuropsychiatric disorders and is currently treated by oral or parenteral administration of exogenous vitamin. Unfortunately, the absorption of orally taken vitamin B12 is low and highly variable, while injections can cause pain and anxiety. Thus, an efficient alternative drug delivery system for overcoming these shortcomings is highly desirable. Novel polymeric microneedle (MN) arrays have the potential for minimally invasive transdermal treatment of vitamin B12 deficiency. Bilayer dissolving MN arrays (19 x 19 needles, 600 µm height) containing 135 µg vitamin B12 were cast using two different aqueous polymer blends. MN arrays showed sufficient mechanical strength for skin insertion, dissolved rapidly and delivered 72.92% of their drug load in vitro over 5 h. Ultimately, the potential of delivering a therapeutically relevant dose of vitamin B12 transdermally was demonstrated in vivo in Sprague-Dawley rats by comparison to subcutaneous injections. Maximum plasma levels of 0.37 µg/mL occurred 30 min post-MN application, highlighting the ability of fabricated MN arrays to rapidly deliver vitamin B12 transdermally.

The focus on novel systems for transdermal delivery of therapeutic agents has increased considerably over recent years, as this administration route comes with many advantages. Polymeric microarray patches (MAPs) are minimally invasive devices that enable systemic delivery of a wide range of drugs by overcoming the outer skin barrier. Conventionally, MAPs fabricated by micromoulding have a low needle density. In this study, the performance of hydrogel-forming MAPs cast using novel industrially manufactured micromoulds with a high needle density (600 needles/0.75 cm2) was compared to that of MAPs obtained using conventional moulds with a lower density (196 needles/0.89 cm2). Surrounding holders for micromoulds were designed for time-efficient fabrication of MAPs. The influence of needle densities on mechanical strength, insertion efficiency and in vitro permeation of ibuprofen sodium (IBU) was analysed. Insertion of both MAPs into an artificial skin model and neonatal porcine skin was comparable. No significant difference was observed in permeation studies of IBU (p > 0.05), with a delivery of 8.7 ± 1.7 mg for low-density and 9.5 ± 0.1 mg for high-density MAPs within 24 h. This highlights the potential of these novel micromoulds for manufacturing polymeric MAPs with a higher needle density for future applications.

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